Electrostatic coating systems for coating car bodies with liquid paint are known, for example, from DE-OS 39 11 454. The coating system described there is a so-called "roof machine" for coating car bodies from above. With this system, the surfaces of car bodies which face upwards are coated, in particular, but the surfaces of the car body which face towards the front and the rear can also be coated with it. Until now, car bodies have usually not been coated with powder, but rather with liquid paint, because smoother surfaces can be achieved with the latter. Liquid coating materials, however, contain solvent and other volatile components, which evaporate on the car body during the spraying process and firing of the liquid paint on the car body, and therefore represent an environmental problem. The part of the liquid coating material which is sprayed past the car bodies is waste. For atomization of liquid coating material, different spray organs are also necessary than for atomization of coating material in powder form, which latter material is passed to the spray organs in an air stream. However, powder has the advantage, as compared with liquid coating materials, that it does not contain any volatile components, so that powder does not result in any environmental problems in this regard. Another difference is that powder which is sprayed past the object to be coated, or bounces off it, can be recovered and reused. Various techniques are known for recycling powder, for example, slanted cabin floors, from which the powder slides out of the cabin into a feed groove arranged next to it, or into a container, conveyor grooves, ductor devices and motor-driven, continuously moving endless filter belts (DE-PS 24 30 517) on the cabin floor. Both for liquid coating material and for powder coating material, the cabin and all flow paths of the coating material must be cleaned very carefully when changing from one kind of material to another kind of material, before the latter can be used. Otherwise, material mixing occurs, resulting in coating defects and color defects. Such a so-called "color change" must take place very rapidly, however, so that little production time is lost for achieving the coating operation. Furthermore, no coating material accumulations, either of liquid material or powder material, are allowed to form within the coating system; these would lead to coating problems on the object to be coated. Furthermore, such material accumulations are also not allowed so as not to cause any explosive material concentrations in the cabins. To prevent powder coating material from accumulating on the cabin walls, interchangeable cabin walls, air-flooded cabin walls, high electrical potential in the cabin walls and cabins with plastic walls (DE-OS 39 19 614) have already become known.
Electrostatic charging of powder is known from DE-PS 20 65 699.